1. Field of the Invention
The invention relates to a turbine for a machine for projecting abrasive for the surface treatment of objects. The invention also relates to a support element for such a turbine, a machine for surface treatment of objects and to the use of such a turbine.
2. Description of Prior Art
Such turbines, also referred to as shot blasting turbines or wheel blasting turbines, are used for the purpose of treating the surface of objects, for instance removing a rust layer from metal objects. Such turbines are embodied to drive a quantity of abrasive, consisting for instance of abrasive grains, such as plastic or metal grains, at high speed in the direction of an object in order to blast the surface of the object, for instance with the purpose of removing a layer of paint or rust or the like present on the object. The abrasive is introduced into the centre of a rotating turbine, after which a number of blades arranged in the turbine entrain the abrasive. The abrasive leaves the turbine via the radial side thereof.
Examples of such shot blasting turbines are described in the patent documents WO 2011/123906 A1, WO 2011/107204 A1, EP 1 543 922 A1 and GB 2 276 341 A. The turbines in WO 2011/123906 A1 and EP 1 543 922 A1 are provided with substantially straight, radially extending impeller blades or forward curved impeller blades. The forward curved blades have the advantage, among others, relative to the straight blades that at a constant rotation speed of the turbine wheel more kinetic energy can be imparted to the abrasive. Described in EP 1 543 922 A1 is a shot blasting machines in which impeller blades are applied having a substantially Y-shaped guide surface. An advantage of this type of impeller blade is that the turbine can be rotated both left and right in order to project the abrasive.
The blades of the turbines are manufactured from a hard wear-resistant material because of the high wear resistance required in order to maintain a relatively high uptime.
The turbine described in GB 2 276 341 has blades wherein each of the blades are mounted via two elongate studs (FIG. 11) provided on either side in corresponding recesses in the flanges of the turbine wheel. A drawback of this mounting method is that, as a result of a relatively small contact width, i.e. the distance (width) over which the blade is supported with the studs on either side by the flanges, is relatively small. The contact width corresponds roughly to the width of the studs themselves.
The turbine described in the document DE 1 062 570 B has a similar drawback. The blades are supported in radial recesses in the flanges of the turbine. The blades are supported only at the position of their longitudinal edges. The blades of the turbine described in EP 1 352 713 A1 have studs on their longitudinal sides which can be arranged in radial recesses in the flanges. This means that the blades are supported only via the lateral studs.
Known from the British patent GB 743 381 A is a turbine with blades which are supported only on one side. The turbine has a single flange, wherein an L-shaped support is screwed fixedly to the flange. The L-shaped support is placed behind a blade and supports it during rotation of the turbine. The support can extend behind the whole width of the blade. The support itself will however begin to bend under the influence of the (centrifugal) forces, so that relatively large peak stresses will in turn also occur at the position of the connection of the blade and the support to the flange. These peak stresses can cause wear and thereby limit the lifespan of the turbine. Cases are even known where the peak stresses have resulted in damage to the blades, or even breaking thereof.
Also described in U.S. Pat. No. 3,936,979 is a turbine supported on only one side. The turbine has a single rotor plate to which a bracket is screwed. The support has an L-shaped cross-section and supports the blade over only a part of the width thereof. The known turbine therefore also has relatively high peak stresses in the blade, particularly close to the connection of the support to the rotor plate.
In the shot blasting machine described in document EP 1 543 922 A1 each of the blades is also supported on the side walls of the turbine with a relatively small contact width. Owing to the limited contact width each blade has relatively small supporting surfaces with which the blade is supported by the flanges. The consequence hereof is that relatively high stresses occur in the material of the blade, and in particular at the position of the edge of the supporting surfaces. In practice these stresses limit the maximum dimensions of the turbine.
A further drawback of the known shot blasting machine is that the mounting of the blades on the flanges, for instance the above stated elongate studs on either side of the guide surface of the blades, and thereby the supporting surfaces with which the blades are supported, can wear during use due to abrasive passing therealong. Wear also occurs when the blades and the associated mounting are manufactured from a hardened material. This may mean that the blades are already so worn after relatively short-lived use that they have to be replaced.
A further drawback of the known blades is that the blades themselves are mounted directly on the flanges of the turbine. When a blade has to be replaced, for instance because it is worn, this often means in practice that the whole turbine wheel must be disassembled to enable removal of the blade from the turbine part. This is labour-intensive and also limits the available uptime of the shot blasting machine.
A further drawback of the known shot blasting machines is that, due to the decrease in the mass of the component, for instance a blade, particularly at determined locations where wear is greater than elsewhere, imbalance can occur in the turbine. If the imbalance in the turbine becomes too great, this can have an adverse effect on the bearing-mounting of the turbine. This can result in the turbine having to be reconditioned, this entailing high cost and less available uptime.
The application of wear-resistant materials in the known blades has the further drawback that such wear-resistant materials, such as ceramic or hard metal, have a poor dimensional stability. It is difficult, and at the very least highly costly, to manufacture a blade which has on the one hand a high wear resistance and can on the other be precisely manufactured such that little play occurs in the turbine, for instance at the position of the connection of the blade to the flanges of the turbine. The application of blades of ceramic material or hard metal means in practice that a relatively large amount of play occurs, which can result in imbalance in the turbine.
It is an object of the present invention to provide a turbine, mounting and/or machine in which at least one of the above stated drawbacks is obviated or reduced.
Is also an object of the invention to provide a turbine, mounting and/or machine in which the stresses at the location of the supporting surfaces can be reduced.
It is also an object of the invention to provide a turbine, mounting and/or machine with an extended available uptime.
It is also an object of the invention to provide a turbine, mounting and/or machine in which the blade element can be removed or exchanged quickly and easily, wherein particularly the turbine, or even the turbine wheel itself, need not be disassembled.
It is a further object of the invention to provide a turbine, mounting and/or machine which has relatively little problem with imbalance, even after prolonged wear due to the abrasive.